Get Rid of Bad Branches
When pruning bushes, remember what some arborists call the “4 Ds.” Start with the dead and damaged branches, because they make the plant look bad, and encourage rot and disease. Also, cut out wilted, dried or diseased branches as soon as you spot them, to remove disease before it spreads. “Deranged” includes a broad range of branches that cross (the rubbing wears away the bark), loop down to the ground or simply look out of character with the bush (stick out at an odd angle or grow alongside the trunk). This pruning also thins out the bush, opening its interior to more light and air, which encourages fuller, healthier growth.
Prune One-Third of a Bush's Canes
Cane-type bushes, such as forsythia and hydrangea, usually send up new canes from their roots every year. In general, prune out the oldest (larger) wood to control the bush height. It's also OK to trim out newer canes to thin the interior of the plant and let in light, as well as to control spread. If one of these bushes has gotten too big and out of control, you can often cut off all the canes and the roots will send up new shoots. You'll have a nice new bush in a year or two. Note: All bush categories have exceptions to these rules. So know your plants!